Trapped on Dave's back, Nate couldn't see what his boyfriend (or rather, captor) was adding to himself, but he could certainly hear it. With four arms, the furious clicking and typing was twice as loud, and stretched on twice as long, until it all went silent. One of Dave's heads craned around to look at Nate. "Ready for my new form?"
He tried to shake his head, but Dave's grip wouldn't allow it. A crazed grin spread over the humantaur's face as a final click resounded around the room. "Hold on tight, you're gonna feel this one."
Nate watched as a dark hue began to spread down from Dave's heads to his toes, turning his entire body a midnight black. Beneath his back, he could feel Dave's skin hardening to something tougher than diamond. Black armour plates worked their way across Dave's body, covering his hypermuscular form in a shiny, hard coating until his entire body looked as if it was carved of obsidian. At the edges of his armour, sharp blades arose, strong enough to cut through any material known to man.
Dave's necks were the next things to change, and they grew longer and longer, holding his two heads aloft on thick, muscular tentacles, each six feet long. A third head soon grew to join the two, and each of their four eyes duplicated to eight before their iris melted away and their pupil grew slitted, the rest of their eye becoming a solid, glowing red. Black, scaly hoods replaced hair as the serpentine heads circled Nate, like cobras ready to strike. At the fear on his face, Dave opened his mouths for a hissing laugh, showing his six, six-foot tongues growing dark and forked, like a snake's. They ran over his fangs, then his second, third and fourth sets of sharp teeth, which filled his entire mouths.
But, the changes didn't stop there. Now able to watch all parts of his body at once, Dave hissed in delight as he watched his changes continue. From his tailbone, three thick, long scorpion tails extended, each one tipped with a dangerously sharp barb. He licked his lips, tasting the venom dripping from his fangs. The one in his tails was ten times as potent. He glanced down as the arms holding Nate down transformed along with his legs, becoming long and spindly, tapering to a needle-thin point. His eight spider legs clacked in delight as his four cocks became tentacles, long and prehensile as his tongues, and his armoured ballsack grew even more as the muscular appendages thickened.
Dave watched as two more pairs of arms grew on his torso, directly behind his first two pairs so he had one arm facing in either direction, able to hold his squirming boyfriend down as the final transformation started.
From his shoulder blades and his spidertaur body, two nubs began to poke out. They grew in size quickly, five long, skeletal fingers quickly wrapped in black leather and then the same armoured coating the rest of his body had. His two pairs of dragon wings flapped as he gave a triumphant hiss, rearing up on his back two legs. Breathless, he let himself down and extracted Nate from the back of his spidertaur body, where he was nestled between the joints of the wings.
"Ssso, how do you like it?" Dave asked as he gave a demonstration of his new body, scuttling around the tiny boy on his new legs. Nate didn't reply. He was cowering on the floor with his head tucked in his hands.
"What'sss wrong? I thought you were kinda into the monssster fucking genre?" No reply.
He lowered one of his heads down to Nate, speaking softly through only one of his mouths this time. "Hey, I can change back. We can go back to how it was before. You can be your larger self, and I can be your plain, humantaur boyfriend again."
Still, Nate didn't react. He was just rocking back and forth in a fetal position on the floor, eyes shut tight. Dave's heat-sensing pits under his nose sprang to life. Nate's body temperature was elevated higher than normal, and his tongues detected higher levels of cortisol. His boyfriend really was sick. Luckily, he knew just how to help him.
Mentally switching the venom in his tails to a light sedative (rather than the reality-bending aphrodisiac it had previously been), he plunged the barb into Nate's neck and watched as his tiny body went limp.
In his strong, armoured arms, he carried the sleeping boy over to the couch, carefully laying him down, before turning back to the computer. "Don't worry, little one. I'll fix you."